系统规格，已格式化，便于阅读。我将在底部添加我拥有的与 Plasma 相关的软件包，因为它很长。
[][]uname -a
>Linux kublai-1888 4.18.0-15-generic #16-Ubuntu
>SMP Thu Feb 7 10:56:39 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
[][]nvidia-smi
>Driver Version: 390.87
>(downgraded from 415 which previously worked on a different
>installation because I was not able to switch off of Nouveau)
[][]apt list --installed | grep sddm
kde-config-sddm/cosmic,now 4:5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed]
sddm-theme-breeze/cosmic,now 4:5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
sddm/cosmic,now 0.18.0-1ubuntu2 amd64 [installed,automatic]
我可以正常登录。GPU 设置为我的 960M GPU，经测试为活动 GPU，Nouveau 未被列入黑名单。问题是图形故障、Baloo 出错、无法安装主题以及对系统稳定性的担忧，我在 4.15 之后没有遇到过这些问题。重新安装 sddm 也无济于事。
输出sddm sddm-kcm：
[16:21:09.821] (II) DAEMON: Initializing...
[16:21:09.825] (II) DAEMON: Starting...
[16:21:09.825] (II) DAEMON: Logind interface found
[16:21:09.827] (II) DAEMON: Adding new display on vt 1 ...
[16:21:09.827] (II) DAEMON: Loading theme configuration from ""
[16:21:09.827] (II) DAEMON: Display server starting...
[16:21:09.828] (II) DAEMON: Running: /usr/bin/X -nolisten tcp -auth /var/run/sddm/{30a829c0-5160-4354-bc03-36bc14b823b3} -background none -noreset -displayfd 16 -seat seat0 vt1
[16:21:09.829] (EE) DAEMON: Failed to read display number from pipe
[16:21:09.830] (EE) DAEMON: Display server failed to start. Exiting
Aborted (core dumped)
发出命令sudo sddm sddm-kcm会挂起，并且要求我拥有配置文件的所有权，否则我会遇到接口问题。在 TTY 中发出这些命令会service sddm stop返回未找到显示，这是必然的。
我还缺少以下提到的文件man sddm.conf：
visitor@visitor-69:~$ /usr/lib/sddm/sddm.conf.d
bash: /usr/lib/sddm/sddm.conf.d: No such file or directory
visitor@visitor-69:~$ /etc/sddm.conf.d
bash: /etc/sddm.conf.d: No such file or directory
visitor@visitor-69:~$ /etc/sddm.conf
bash: /etc/sddm.conf: No such file or directory
visitor@visitor-69:~$
跑步whereis sddm.conf回报：
sddm：/usr/bin/sddm/usr/lib/x86_64-linux-gnu/sddm/etc/sddm/usr/共享/sddm/usr/share/man/man1/sddm.1.gz
为方便查看，以粗体显示。
/usr/bin/sddm：第一个结果是应用程序。
/usr/lib/x86_64-linux-gnu/sddm：包含名为 的文件的目录sddm-helper，运行 时会返回相同的错误sddm sddm-helper
。
/etc/sddm：包含一个文件 Xsession，我将把它添加到底部。
/usr/share/sddm：包含 wayland-session Xsession Xsetup Xstop
/usr/share/man/man1/sddm.1.gz：包含一个 .conf，我认为这是默认的。tl;dr我想知道是否应该用它来替换所有丢失的 sddm.confs。
以下是一个示例：
$ apt 列表--已安装|grep plasma
kdeplasma-addons-data/cosmic,cosmic,now 4:5.15.1-0ubuntu1~ubuntu18.10~ppa1 all [installed,automatic]
libkf5plasma-dev/cosmic,now 5.54.0-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed]
libkf5plasma-doc/cosmic,cosmic,now 5.54.0-0ubuntu1~ubuntu18.10~ppa1 all [installed]
libkf5plasma5/cosmic,now 5.54.0-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
libkf5plasmaquick5/cosmic,now 5.54.0-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
libplasma-geolocation-interface5/cosmic,now 4:5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
libplasma3/cosmic,now 4:4.14.38-0ubuntu6 amd64 [installed,automatic]
plasma-browser-integration/cosmic,now 5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
plasma-dataengines-addons/cosmic,now 4:5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
plasma-desktop-data/cosmic,cosmic,now 4:5.15.1-0ubuntu1~ubuntu18.10~ppa1 all [installed,automatic]
plasma-desktop/cosmic,now 4:5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
plasma-discover-common/cosmic,cosmic,now 5.15.1-0ubuntu1~ubuntu18.10~ppa1 all [installed,automatic]
plasma-discover-snap-backend/cosmic,now 5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
plasma-discover/cosmic,now 5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
plasma-framework/cosmic,now 5.54.0-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
plasma-integration/cosmic,now 5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
plasma-nm/cosmic,now 4:5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
plasma-pa/cosmic,now 4:5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
plasma-runners-addons/cosmic,now 4:5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
plasma-scriptengine-javascript/cosmic,now 4:17.08.3-0ubuntu2 amd64 [installed,automatic]
plasma-vault/cosmic,now 5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
plasma-wallpapers-addons/cosmic,now 4:5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
plasma-widgets-addons/cosmic,now 4:5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
plasma-workspace/cosmic,now 4:5.15.1-0ubuntu1~ubuntu18.10~ppa1 amd64 [installed,automatic]
/usr/share/man/man1/sddm.1.gz，提取到sddm.conf.5：
.\" Man page generated from reStructuredText.
.
.TH SDDM.CONF 5 "August 2015" "sddm 0.18.0" "sddm"
.SH NAME
sddm.conf \- sddm display manager configuration
.
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.SH SYNOPSIS
.sp
Configuration loads all files in the configuration directories followed by the configuration file in the order listed below with the latter having the most precedent. Changes should be made to the local configurations.
.INDENT 0.0
.TP
.B \fB/usr/lib/sddm/sddm.conf.d\fP
System configuration directory
.TP
.B \fB/etc/sddm.conf.d\fP
Local configuration directory
.TP
.B \fB/etc/sddm.conf\fP
Local configuration file for compatibility
.UNINDENT
.SH DESCRIPTION
.sp
This file configures various parameters of the sddm display manager \fBsddm\fP(1).
If this file is not available, default values are used.
.SH OPTIONS
.sp
[General] section:
.INDENT 0.0
.TP
.B \fIHaltCommand=\fP
Halt command.
Default value is "/bin/systemctl poweroff".
.TP
.B \fIRebootCommand=\fP
Reboot command.
Default value is "/bin/systemctl reboot".
.TP
.B \fINumlock=\fP
Change numlock state when \fBsddm\-greeter\fP starts.
Valid values are \fIon\fP, \fIoff\fP or \fInone\fP\&.
If property is set to \fInone\fP, numlock won\(aqt be changed.
Default value is "none".
.TP
.B \fIInputMethod=\fP
Set the Qt input method for the greeter.
Tablet users with Qt Virtual Keyboard installed can set this
to "qtvirtualkeyboard" for the on\-screen keyboard.
Other known values are "ibus" for the Intelligent Input Bus,
or "compose" for dead keys support.
Leave this empty if unsure.
.TP
.B \fINamespaces=\fP
Comma\-separated list of paths bound to Linux namespaces to enter with
setns() before starting the user session. For example, to enter network
namespace \fImynet\fP created with \fIip netns add mynet\fP, the value might be
\fI/run/netns/mynet\fP\&. Default value is empty. (The value is ignored if
the operating system is not Linux.)
.UNINDENT
.sp
[Theme] section:
.INDENT 0.0
.TP
.B \fIThemeDir=\fP
Path of the directory containing theme files.
Default value is "/usr/share/sddm/themes".
.TP
.B \fICurrent=\fP
Name of the current theme.
By default this setting is empty, meaning the embedded theme
will be used.
.TP
.B \fIFacesDir=\fP
Path of the directory containing face files,
face files should be in username.face.icon format.
Default value is "/usr/share/sddm/faces".
.TP
.B \fICursorTheme=\fP
Name of the cursor theme to be set before starting
the display server.
.TP
.B \fIEnableAvatars=\fP
When enabled, home directories are searched for ".face.icon" images to
display as their avatars. This can be slow on some file systems.
When disabled, all avatars will be default. Themes may choose to hide
them altogether.
Default value is true.
.UNINDENT
.sp
[X11] section:
.INDENT 0.0
.TP
.B \fIServerPath=\fP
Path of the X server.
Default value is "/usr/bin/X".
.TP
.B \fIServerArguments=\fP
Arguments to the X server.
Default value is "\-nolisten tcp".
.TP
.B \fIXephyrPath=\fP
Path of the Xephyr.
Default value is "/usr/bin/Xephyr".
.TP
.B \fIXauthPath=\fP
Path of the Xauth.
Default value is "/usr/bin/xauth".
.TP
.B \fISessionDir=\fP
Path of the directory containing session files.
Default value is "/usr/share/xsessions".
.TP
.B \fISessionCommand=\fP
Path of script to execute when starting the user session. This script
receives the value of the "Exec" setting in the ".desktop" file of the selected
session and runs it.
Default value is "/etc/sddm/Xsession".
.TP
.B \fISessionLogFile=\fP
Path to the user session log file, relative to the home directory.
Default value is ".local/share/sddm/xorg\-session.log".
.TP
.B \fIUserAuthFile=\fP
Path to the Xauthority file, relative to the home directory.
Default value is ".Xauthority".
.TP
.B \fIDisplayCommand=\fP
Path of script to execute when starting the display server.
Default value is "/usr/share/sddm/scripts/Xsetup".
.TP
.B \fIDisplayStopCommand=\fP
Path of script to execute when stopping the display server.
Default value is "/usr/share/sddm/scripts/Xstop".
.TP
.B \fIMinimumVT=\fP
Minimum virtual terminal number that will be used
by the first display. Virtual terminal number will
increase as new displays added.
Default value is 1.
.TP
.B \fIEnableHiDPI=\fP
Enables Qt\(aqs automatic HiDPI scaling.
Can be either "true" or "false".
Default value is "false".
.UNINDENT
.sp
[Wayland] section:
.INDENT 0.0
.TP
.B \fISessionDir=\fP
Path of the directory containing session files.
Default value is "/usr/share/wayland\-sessions".
.TP
.B \fISessionCommand=\fP
Path of script to execute when starting the user session. This script
receives the value of the "Exec" setting in the ".desktop" file of the selected
session and run it.
Default value is "/usr/share/sddm/scripts/wayland\-session".
.TP
.B \fISessionLogFile=\fP
Path to the user session log file, relative to the home directory.
Default value is ".local/share/sddm/wayland\-session.log".
.TP
.B \fIEnableHiDPI=\fP
Enables Qt\(aqs automatic HiDPI scaling.
Can be either "true" or "false".
Default value is "false".
.UNINDENT
.sp
[Users] section:
.INDENT 0.0
.TP
.B \fIDefaultPath=\fP
Default path to set after successfully logging in.
This is also where SDDM looks for programs.
Default value is "/bin:/usr/bin".
.TP
.B \fIMinimumUid=\fP
Minimum user id of the users to be listed in the
user interface.
Default value is 1000.
.TP
.B \fIMaximumUid=\fP
Maximum user id of the users to be listed in the
user interface.
Default value is 60000
.TP
.B \fIHideUsers=\fP
Comma\-separated list of Users that shouldn\(aqt show up in the user list.
Default value is empty.
.TP
.B \fIHideShells=\fP
Comma\-separated list of Shells of users that shouldn\(aqt show up in the user list.
Default value is empty.
.TP
.B \fIRememberLastUser=\fP
If this flag is true, LastUser value will updated
on every successful login, if false last user value
won\(aqt be updated.
Default value is true.
.TP
.B \fIRememberLastSession=\fP
If this flag is true, LastSession value will updated
on every successful login, if false last session value
won\(aqt be updated.
Default value is true.
.UNINDENT
.sp
[Autologin] section:
.INDENT 0.0
.TP
.B \fIUser=\fP
Name of the user to automatically log in when the
system starts first time.
Default value is empty.
.TP
.B \fISession=\fP
Name of the session to automatically log in when the
system starts first time.
Default value is empty.
.TP
.B \fIRelogin=\fP
If true and User and Session are set automatic login will
kick in again on session exit, otherwise it will work
only the first time.
Default value is false.
.UNINDENT
.SH SEE ALSO
.sp
\fBsddm\fP(1)
.sp
The full documentation for sddm is available at \fI\%https://github.com/sddm/sddm\fP
.\" Generated by docutils manpage writer.
.